1. Field of the Invention
The present invention generally relates to rotodynamic or centrifugal pumps, and more particularly to rotodynamic pumps having an electro-magnet coupling.
2. Discussion of the Prior Art
In many pumping applications, it is desirable to avoid rotating seals. Rotodynamic pumps have been developed with electro-magnet couplings that utilize an impeller that is driven via a non-contacting electro-magnet coupling in a radial magnet orientation. Such pumps frequently are referred to as being sealless, but actually include a stationary coupling component, and a rotating coupling component that are separated by a canister that is sealed with a static seal. Electro-magnet coupled rotodynamic pumps typically are of one of three types: close coupled; pump and motor separated by a thermal barrier; and vertical submerged.
Close coupled electro-magnet coupled rotodynamic pumps have an electro-magnet coupling that is mounted in a position that is behind the impeller. This may be referred to as a pump having an overhung impeller design. The overhung impeller design has the impeller mounted forward of and spaced from the electro-magnet coupling. The pump and the frame that supports the driving electro-magnet coupling generally are mounted on a common base plate. Rotodynamic pumps having the pump and motor separated by a thermal barrier generally are somewhat similar to close coupled electro-magnet coupled rotodynamic pumps but additionally have the electro-magnet coupling separated from the impeller by a thermal barrier air space. Vertical submerged electro-magnet coupled rotodynamic pumps generally also are of somewhat similar construction to the close coupled version, but the impeller is mounted on the lower end of a vertical shaft. The drive section utilizes an electro-magnet coupling to transmit power to the shaft and impeller.
Radial electro-magnet couplings are common in each of the above rotodynamic pumps, which may otherwise be referred to as kinetic or centrifugal pumps. The radial electro-magnet couplings consist of three main components: a stationary coupling component, such as a stator having multiple electro-magnets; a rotating coupling component, such as an armature with multiple magnets, either of the permanent or induced type; and a containment canister, such as a shroud or barrier separating the stationary and rotating components and forming a boundary of the pump's fluid chamber. The canister often is attached to the housing of the stationary component, such as an outer magnet or outer rotor, with multiple permanent magnets on its inner surface.
Radial electro-magnet couplings utilize a controller that energizes electro-magnets in the stationary component in a rotary sequence to create a rotating magnetic field. The magnetic field of the rotating component aligns and synchronizes with the rotating filed of the stationary component, such that the rotating component is forced to rotate with the rotating field of the stationary component, and drives the pump's impeller, such as a rotor. But neither of the inner or outer electro-magnet coupling components physically touches the other, and the rotating component rotates in a separate environment from the stationary component, separated by the canister.
The radial electro-magnetic couplings are of two configurations, “outer drive” and “inner drive”. Most radial electro-magnet couplings in rotodynamic pumps have an outer drive arrangement in which the stationary component is larger than the rotating component and the stationary component is outside of the pump's fluid chamber. In such configurations, the inner rotating component is smaller than the stationary component and is disposed inside the pump's fluid chamber and is connected to the impeller. The containment canister provides the boundary of the pump's fluid chamber, with the fluid chamber being inside of the canister.
Although less common, some pumps have an inner drive arrangement, which utilizes the same three general components, but the roles are reversed. With an inner drive arrangement, the stationary component is smaller than the rotating component and is outside of the pump's fluid chamber. In turn, the rotating coupling component is larger than the stationary component and is disposed inside the pump's fluid chamber. The rotating component also is connected to the impeller. A containment canister again provides the boundary of the pump's fluid chamber, with the fluid chamber being outside of the canister. All of the inner drive electro-magnet rotodynamic pumps known to the inventors have a common configuration with respect to the location of the impeller relative to the electro-magnet coupling, with the impeller being positioned axially forward of the electro-magnetic coupling.
With the impeller being positioned forward of the electro-magnet coupling, such inner drive pumps have several disadvantages. The pumps are rather large, given that the axial space for the impeller is separate and forward of the axial space for the electro-magnet coupling. The relatively large pumps further require large and more expensive components, a large volume of space for mounting, and such pumps are heavier and more difficult to handle. The inner drive pumps also often experience an impeller thrust imbalance. The impeller is subjected to a high forward thrust load, due to the higher discharge pressure acting upon a relatively large rear surface of the impeller.
The prior art pumps also tend to have additional internal cavities where fluid can stagnate and which often must be flushed out between usages. In addition, the prior art pumps do not provide very effective cooling for the stator or canister, because the canister is not directly exposed to the incoming cool liquid that enters the pump through the inlet port. Canister cooling for such pumps is particularly important when the canister is made from electrically conductive materials, because such materials generate eddy current heating when the magnetic coupling is rotating.
Most of the existing inner drive electro-magnet coupled pump designs include an internal recirculation path, which allows a small amount of pumped fluid to flow from a higher pressure area (near the outlet port) to a lower pressure area (near the inlet port). Such a recirculation path serves three purposes: to prevent stagnation or solids accumulation within the pump; to improve cooling and/or lubrication of the impeller support bearings; and to improve cooling of the stator.
The details of existing recirculation paths vary widely among different pump designs and incorporate many different section designs. However, such internal recirculation paths tend to be rather complex, because they need to flow through an electro-magnet chamber located deep behind the impeller. The internal recirculation paths often include some sections where all the surfaces are stationary. The stationary sections more easily allow product stagnation and/or accumulation of solids.
The present disclosure addresses shortcomings in prior art pumping systems, while providing rotodynamic pumps having an electro-magnet coupling inside an impeller. The disclosure of inner drive pumps includes significant advantages over prior art pumps.